This invention relates to insulating support means mounting high voltage bus conductors where they pass through openings in a grounded metal wall. The invention is particularly concerned with insulating support means of this type that can withstand without damage the abruptly-varying high forces produced by high short-circuit currents such as 60,000 to 80,000 r.m.s. asymmetrical amperes.
In certain types of electrical equipment that include such insulating support means, it is required that the support means include porcelain as an essential element. This requirement is based, in part, upon recognition of the outstanding dielectric properties of porcelain, particularly its excellent long-term resistance to creep-tracking under adverse environmental conditions. While porcelain has excellent dielectric properties, its ability to withstand the impact forces developed by high short-circuit currents leaves something to be desired, particularly if these forces load the porcelain in tension or bending.
To illustrate this latter point, reference is made to certain tests that we have made with support means that comprises a porcelain sleeve around each bus conductor of a three-phase circuit in the region where the bus conductor passes through a grounded metal wall. In this support means, the porcelain sleeve loosely surrounded its associated bus conductor. When subjected to short-circuit currents, it was found that the porcelain sleeves were fracturing at about 60,000 r.m.s. amperes asymmetrical.